1. Field of the Invention
The present invention relates to a stepping motor control system, and more particularly to a stepping motor control system operating a motor in a plurality of operation modes, that is, when an operation is conducted by slow up/down means or when a constant speed operation is conducted at a plurality of speeds.
2. Related Background Art
A constant voltage drive system has been known as a stepping motor drive system. Because this system had the simplest circuit configuration and is most inexpensive, it has been widely used.
On the other hand, a constant current system has been known as a drive system for producing a high speed rotation. In this system, a current flowing in a motor winding is detected to control it to a preset current level by driving a switching device such as a transistor by pulse width modulation.
However, in a stepping motor drive circuit using by the former constant voltage system, when the drive frequency of the stepping motor rises, the rise of the current is slow due to the inductance of the motor winding, which causes a reduction of a torque. As a result, a high speed rotation is not attained.
In the latter constant current system, the high speed operation of the motor is attained but because of necessity of the current detection function, the circuit is complex and its cost is high .
In general, the higher the rotation speed of the stepping motor, the smaller the generated torque . Accordingly, when the current is set to generate the torque required in a high speed rotation mode, the motor vibrates in a low rotation speed mode because of an excessive torque and noise is readily generated. In order to solve this problem , it is necessary to set different current levels in accordance with the rotation speed. This increases the complexity of the circuit .